Since they knew that seniors are apt to injury, the

Since they knew that seniors are apt to injury, the architect of the retirement home designed its staircases with secure railings.

(A) Since they knew that seniors are apt to injury,
(B) Having known that seniors are apt to injury,
(C) Seniors being apt to injury,
(D) Knowing that seniors are apt to injury,
(E) Since seniors are known to be more apt to injury,

OA D

Source: Veritas Prep